Titanium oxide pigments

ABSTRACT

The production of pigmentary TiO2 of improved properties by treatment of TiO2 with combined oxides of silicon and aluminum, the oxides being used in a weight ratio of 5-6 and in a concentration such that the pigment will have at least 0.5 percent by weight of oxide coating.

United States Patent Sheehan et a]. 51 Apr. 25, 19 72 54] TITANIUM OXIDE PIGMENTS [56] References Cited [72] Inventors: Gerard Marlin Sheehan; George UNITED STATES PATENTS Leathwhite Roberts, Jr., both of Lynchburg, Va; Paul Montgomery 3,035,966 5/1962 Sluta ..106/300 x Dupree, B ki Rid 3,345,187 10/1967 Binnis ....106/300 X 3,383,231 5/1968 Allan ..l06/300 [73] Assignee. (A grnesican Cyanamld Company, Stamford, 3.410'708 H968 McGinnis nmlo/soo 3,437,502 4/ l 969 Werner .1 106/300 Filed! Aug- 7, 1969 3,449,271 6/1969 O'Connor et a1. 106/300 [21] Appl. No.: 848,353 I Primary Examiner-Tobias F. Levow Related U-S- Application Data Assistant Examiner-H. M. S. Sneed [63] Continuation-impart of Ser. No. 625,618, Mar. 24,

[57] ABSTRACT [52] US. Cl. ..l06/300, 106/308 B, log/(315L811? The production of pigmentary Tiog of improved propertiesby [5]] Int Cl C09c U36 treatment of TiO, with combined oxides of silicon and alu- 5s neiee?eeeei;IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIiIII'i/oo 308B mime,theoxidesbeingusedinaweighmfioofs-fiandm concentration such that the pigment will have at least 0.5 percent by weight of oxide coating.

4 Claims, No Drawings TITANIUM OXIDE PIGMENTS This application is a continuation-in-part of application Ser. No. 625,618, filed Mar. 24, 1967.

This invention relates to improved pigmentary titanium dioxide. It relates further to TiO pigments of enhanced physical properties, including brightness, ease of dispersibility, and color tone, for use in enamels, latex paints and other plastic substrates, especially vinyl asbestos tiles. More particularly, the present invention relates to a process for treating finely divided hydroclassified TiO with a specially proportioned combination of hydrous oxides of silicon and aluminum whereby pigmentary TiO of the above-defined nature is obtained.

It isknown that TiO pigmented resinous materials-can be stabilized by the use of pigment coated with hydrous oxides of silicon and aluminum. This is disclosed in US. Pat. No. 3,035,966, issued May 22, l962, as a means of improving the resistance of pigmented resins, especially paper laminates, to discoloration by sunlight. In accordance with the patent, the

preferred way of preparing the stabilized pigmented resinous compositions is by admixing a slurry of the TiO pigment and the two hydrous oxides in a ratio such that from i-2 moles of alumina are present for each mole of silica and the combination of hydrous oxides is in a concentration equal to 2-15 percent of the weight of the TiO,. The use of equimolar amounts of silica and alumina is shown to give the greatest protection of any other silica-alumina combination although the effectiveness of a given mixture of hydrous oxides seemed from the data to depend upon the concentration of hydrous oxides in the coating composition. At any rate, relatively high percentages of hydrous oxides were used to attain the sought-after light stability.

It is an object of the present invention to provide a method of improving the usefulness of TiO: pigment in. plastic applicas tions where brightness and ease of dispersibility are important considerations in addition to the conventionally recognized need for good light fastness. It is a further object of this invention to provide TiO pigment of enhanced physical characteristics as prepared by the process of the present invention.

In accordance with this invention, these and other objects are achieved by treating TiO particles with a mixture of hydrous oxides of silicon and aluminum in a proportion such that at least about four parts of silica are used for each part of alumina and in an amount such that the treatment with the combined oxides employs at least 0.5 weight percent based. on the weight of the untreated TiO The ratio of silica to alumina, preferably, should be in the range of about 5-6 parts of silica based on the. weight of alumina. lt is critical, however, that at least about 0.5 percent of silica be employed in treating the TiO When less than this percent is used, it is found that brightness of the final pigmentary material is-reduced considerably. Thus, in accordance with the present invention, the improved TiO pigment must contain a minimum concentration of silica and a definite amount of alumina, the amount being proportioned on the concentration of silica. Surprisingly, both enhanced brightness and color tone are obtainable only under the critically defined proportions and concentrations discovered in accordance with the present invention. When, for example, a given amount of silica is present in the TiO composition, the degree of brightness may vary considerably depending upon the proportionate concentration of alumina. It is similarly surprising'that the use of silica and alumina in a ratio of five or greater does not result in plastic compositions of desired brightness and color tone when the minimum concentration of silica required by this invention is not present in the final TiO, pigment.

This invention may be used to improve pigmentary TiO either anatase or rutile structure, obtained by conventional methods involving calcination of titania hydrolysates (i.e., pigmentary TiO from the sulfate" process); or combustion of titanium tetrachloride (i.e., TiO, from the chloride" process); or high temperature hydrolysis of titanium tetrachloride. From the above methods, an aqueous slurry of TiO pigment is obtained at any desired solids content e.g., percent to 30 percent by weight). In usual practice, the slurry is treated with'a small amount of sodium hydroxide (0.05 percent by weight of Tio or other dispersing agent for the purpose of deflocculation and is then hydroclassified by any convenient technique to eliminate particles coarser than about four microns. The hydroclassified particles thus obtained are subjectedto treatment with hydrous oxides of silicon and aluminum whereby the -TiO pigment is improved in the aforementioned respects. Generally, treatment with thecombined hydrous oxides may be followed immediately by dewatering; or first by aging at any temperature in the range of 5-l00 C. forv periods up to about 24 hours and then dewatering. The dewatered oxide-treated TiO is then washed substantially free of soluble salts and dried. The resulting cake can be broken up by conventional milling means. One especially suitable procedurefor accomplishing this end is fluid energy milling as carried out in a Reductionizer or Micronizer with either air or super-heated steam at a temperature of above about 450 F. and under a pressure of about -175 p.s.i.g.

The hydrous alumina and silica can be incorporatedwith theTiO by the formation of the hydrous oxides in situ. The procedure may be accomplished for example by the addition of an aluminum salt such as aluminum sulfate. and a soluble silicate, followed by adjustment of pH whereby the hydrous alumina and silica are formed. When both the aluminiferous and siliceous materials have been added to the slurry of titanium dioxide pigment, the mixture may be conditioned by heating to any temperature in the range of room temperature to the boiling pointof the. mixture. Heating may be conducted for several hours although a period of l-3 hours is adequate. After heating, the treated TiO, is filtered, washed substantially free of soluble salts and then dried. The dried pigment may be milled to the desired degree of sub-division by conventional means as aforementioned. Optionally, prior to milling, the TiO pigment may be treated as disclosed in US. Pat. No. 3,015,573 for the purpose of improving dispersibility with materials such as iriethanolamine and ethylhexoic acid.

Suitable sources of hydrous alumina are its water soluble salts which are readily hydrolyzable, such as aluminum sulfate, aluminum chloride and sodium aluminate. Representative sources of hydrous silica are soluble silicates, such as potassium, sodium, and ammonium, and silicic acid sols.

The improved TiO pigment produced by the process of this invention is highly suitable for opacification of plastics, espe' cially vinyl asbestos tile. To test the TiO-, pigments obtained by the present invention, use has been made in the following examples of a Hunter Multi-purpose Reflectometer which determines the brightness and yellowness of samples to be tested. Yellowness is reported in the following examples as yellow factor'which is determined by the following equation:

YellowFactor= (A-B)/G X 100 wherein A AmberReflectance B Blue Reflectance G Green Reflectance Brightnesswas determined as the percent of green light reflected from the test sample when exposedto light from a green filter. A high'yellow factor isindicative of undesirable color tone.

In several of the examples, a Hunter D-25 Color Difference Meter was used to determine the brightness as R which is a measure of green reflectance, and the yellowness as B of the test samples.

The following examples, in which pans and percentages are by weight unless otherwise specified, are presented to further illustrate the present invention.

The concentration of the hydrous oxides are based upon the weight of the TiO' to be treated and are expressed in terms of percent silica and alumina.

EXAMPLE 1 Samples of Ti0 were prepared as follows and tested for brightness and yellowness. Results are reported in Table I. Sample 1A) To a hydro-classified slurry of rutile TiO (700 parts) of about 20 percent solids, was added 0.2 percent SiO, as N brand (Philadelphia Quartz Company) sodium silicate with a SiO,/Na,0 ratio of 3.22. The slurry was then heated to 70 C.

70 C. and neutralized to pH 8.0 with N" brand sodium silicate giving an SiO content of 0.5 percent. After mixing 2 hours at 70 C., filtering and washing, the sample was repulped at about 40 percent solids and treated with 0.1 part each of aqueous aluminum sulfate solution. The slurry was heated to and treated with aluminum sulfate solution, yielding a pH of triethanolamine and ethyl hexoic acid. The slurry was mixed 6.0 and an Al 0 content of 0.03 percent. The slurry was then ne hour at 50 C. and filtered. After dryi g. p e as mixed for 2 hours at 70 C., filtered, washed substantially free twice passed through a 2 In mzer as in Ex mple 1. of soluble salts and dried. After drying the pigment was fluid- Sample energy milled for two passes in a 2 inch Reductionizer with Same 35 (2 except for addmcn of P 2 and steam at 500 F. and 120 p.s.i.g. 1.0 ercent S10 Sample (113) Sample (2C) 7 Same as Sample (1A) except 0.5 percent Si0 as N brand Same as 6X66!)t for addmo" of 063 Percent t and sodium silicate and 0.07 percent A1 0 as aluminum sulfate P zwere added to the TiO slurry. Sample s l (1C) Same as (2A) except for addltlon of 0.4 percent Al,0, and

Same as Sample lA) except 1.0 percent Si0 and 0.14 per- 170 P slow TABLE II cent A1 0 were added to the Ti0 slurry. V l b t n TABLE I l e llito VIipyltasbesosttile meter metere Ratio 553; Percent Percent Percent SiOz/ bright- Yellow Ratio green Sample S102 A120: A1203 11855 fa tor P til i: so b'ht- Yll Sample ?3z ailo r iess f e o r (2A)" o'gABLEgiIg g From the foregoing noted that a It can Seen from T F of increasing belowminimum concentration of sio2 was considerably hydrous oxide content while maintaining a S1O /Al 0 ratio of lower than the other two samples, although its brightness was f to ii f i .3; i s bluentess of satisfactory. Samples (13) and (1C) with the same SiO /Al 0 or one) o e sequen l ten was ratios were, nevertheless, bluer, i.e., less yellow. This example tmued f P because the Slog/A1203 of five thus illustrates that by increasing the silica content the yelwas no mamtame lowness decreases while brightness remains essentially the EXAMPLE 3 same.

Sample (3A) VINYL ASBESTOS TILE PROCEDURE To a hydroclassified slurry of rutile TiO (700 parts) of about 20 percent solids, 1.8 percent A1 0 was added as an b S; gfil iig izglz tz g gg i j i l s gg E Z125: 40 aqueous aluminum chloride solution. The slurry was heated to y d l g y f 2 70 C. and neutralized to pH 7.0 with sodium hydroxide. After g us a mamum e concentranon 0 percent as mixing 2hours at 70 C., and filtering and washing, the sample 0 was repulped at about 40 percent solids and treated with 0.1 b d 0 percent each of triethanolamine and ethylhexoic acid. The $225? zf gf gg 2 slurry was mixed 1 hour at C. and filtered. After drying,

200:0 pans the sample was twice passed through a 2 inch Reductionizer.

Sample (38) The vinyl asbestos compound was banded on a Farrel 2 roll To hydroclasslfled Slurry. of 2 (700 Parts) mill and the titanium dioxide added to the banded material 50 abPut 20 Percent Solldsi l 2 3 as an aqueous while the rolls were turning mlnum sulfate, was added. The slurry was heated to 70 C. and Mill C di i N" brand sodium silicate was added in an amount equivalent R0" Temperature; to 0.6 percent SiO- The pH was then adjusted to 4.0 with From; 305 2 p53) NaOH. After mixing 2 hours at 70 C., and filtering and wash- Back; c (water only) psi 55 ing, the cake was repulped at about 40 percent solids, and Nip Setting; treated with 0.1 percent each of triethanolamine and ethyl:

5 band hexoic acid. The slurry was mixed 1 hour at 50 C., and fil- 15 10 passes) tered. After drying, the sample was twice passed through a 2 (2 passes) inch Reductionizer.

Roll Speed: 60 ample (3C) i From: 46 Same as (38) but for addition of0.9 percent 810,.

Back: 32 f.p.m. Sample (3D) Moldin (Com ression) No shims Same as (3B) but for addition of 1.2 percent SiO, and of In 3 z HCl to maintain a pH of4.0.

J p Sample (315) Preheat 2 minutes (Farrel 4% Inch diameter ram) Same as (3B) but for addition of l 5 percent SiO and of 2 til.tlarsiprease pressure slowly to 11 tons (6 tons for Individual 7 C1 to maimainaPH of4.0.

Cool 7 minutes TABLE In Vinyl asbestos tile D2t5 color EXAMPLE 2 Percent Percent Si02/ me er Sample SiOz A1 03 A1203 RD B1.

Sample (2A) 1. s 42. 0 4.3

To a hydro-classified slurry of rutile TiO, (700 parts) of 3;; 5 12 2:;

about 20 percent solids, 0.1 percent A1 0 was added as an g-g g 25% 2.

Pigment Sample (3E) of this invention is capable of giving the same level of tile brightness obtainable with about 7 percent more of pigment Sample (3A). Thus, pigment Sample (3E) of this invention is significantly more efficient and economical to use.

EXAMPLE 4 Sample (4A) To a hydroclassified slurry of rutile TiO (700 parts) of 20 percent solids, 0.3 percent A1 0 as aluminum sulfate, was added. The slurry was heated to 70 C. and neutralized to pH 7.0 with sodium hydroxide. After mixing 2 hours at 70 C. and filtering and washing the sample was repulped at about 40 percent solids and treated with 0.1 percent each of triethanolamine and ethylhexoic acid. The slurry was mixed 1 hour at 50 C. and filtered. After drying, the sample was twice passed through a 2-inch Reductionizer as in Example 1, Sample 1A).

Sample (4B) To a hydroclassified slurry of rutile TiO (700 parts) of about 20 percent solids, 0.2 percent A1 0 as aluminum sulfate and 0.25 percent of IO percent HCl were added. The slurry was heated to 70 C., and N brand sodium silicate (SiO- ,/Na 3.22 and percent SiO was then added to pH 4.0, yielding a 1.2 percent SiO concentration. After mixing 2 hours at 70 C. and filtering and washing, the sample was repulped at about 40 percent solids treated with 0.1 per cent each of triethanolamine and ethylhexoic acid and completed as for Sample (4A).

The samples were incorporated into vinyl asbestos, molded into tiles and analyzed for brightness and yellowness. The results are given in the following table.

TABLE lV A1203 Rn Percent Percent Sample EXAMPLE 5 To a hydroclassified slurry of rutile TiO (700 parts) of about percent solids, 0.2 percent Al 0 was added as an aqueous aluminum chloride solution and silicic acid sol was then added to a 1.2 percent SiO level. The slurry was heated to 70 C. and neutralized to pH 7.0 with sodium hydroxide. After mixing 2 hours at 70 C., and filtering and washing, the sample was repulped at about 40 percent solids and treated with 0.1 percent each of triethanolamine and ethylhexoic acid. The slurry was mixed 1 hour at 50 C. and filtered. After drying, the sample was twice passed through a 2 inch Reductionizer. The silicic acid was prepared by passing N brand sodium silicate diluted to about 50 g./l. SiO through a column of Dowex 50 cation exchange resin in its hydrogen form.

The resulting TiO was incorporated into vinyl asbestos tile by the above-defined procedure and, upon testing, found to have a brightness (R of 43.0 and a yellowness (8,) of 3.7.

EXAMPLE 6 To a hydroclassified slurry of rutile TiO (700 parts) of 20 percent solids, 0.3 percent M 0, as aluminum sulfate, was added. The slurry was heated to 70 C. and neutralized to pH 7.0 with sodium hydroxide. After mixing 2 hours at 70 C. and filtering and washing, the sample was repulped at about 40 percent solids. Then 1.5 percent SiO as silicic acid sol was added along with 0.1 percent each of triethanolamine and ethylhexoic acid. The silicic acid was prepared by passing N brand sodium silicate, diluted to an SiO content of about 50 gill. through a column of Dowex 50 ion exchanfie resin. The s urry was mixed 1 hour at 50 C. and filtered. fter drying,

EXAMPLE 7 Sample A To a hydroclassified slurry of rutile TiO (700 g.) of about 20 percent solids, 0.3 percent MgSO .7H- O and 0.2% A1 0 as aluminum sulfate were added. Slurry was then heated to 70 C. and neutralized to 7.0 pH with sodium hydroxide. After mixing 2 hours at 70 C., filtering and washing the sample was repulped at about 40 percent solids and treated with 0.1 percent each of triethanolamine and ethylhexoic acid. The slurry was mixed 1 hour at 50 C. and filtered. After drying, the sample was given two passes through a 2-inch Reductionizer with steam at 500 F. and 120 p.s.i.g. Sample B Processed the same as (A) except 1.0 percent Si0 as ammonium silicate was added to repulp along with the triethanolamine and ethylhexoic acid. Sample C Processed the same as (A) except 2.0 percent SiO as ammonium silicate was added to repulp along with triethanolamine and ethylhexoic acid. Results from an evaluation in vinyl asbestos tile were as follows:

Vinyl asbestos tile Hunter I)25 color diff. meter SiOQ A1203 Rn B L 0. 2 55. 7 l. T 5 56. 0 1. 4 10 55. u 1.3

The effect of the invention is to improve strength,

brightness and blueness of tone.

We claim:

1. Pigmentary TiO having enhanced physical properties with respect to brightness, color tone and ease of dispersibility comprising finely divided anhydrous TiO containing a mixture of hydrous oxides of silicon and aluminum in a proportion such that at least about 5 weight parts of silica are used for each part of alumina and at least 0.5 parts of combined oxides are used for each parts of untreated TiO;.

2. A process for the preparation of the pigment of claim 1 which comprises treating a slurry of TiO with an aqueous solution of an aluminum salt to give an acidic slurry which is neutralized and admixed with a silica containing material in a proportion such that at least about 5 weight parts of silica is present for each part of alumina whereby a mixture of hydrous oxides of silicon and aluminum is precipitated; conditioning the coated TiO pigment by aging at a temperature ranging from 5 to 100 C. for a period up to about 24 hours; washing said conditioned pigment with water until it is substantially free of soluble salts; drying said pigment at an elevated temperature; and then milling said dried pigment until it has reached the desired degree of sub-division and is suitable for pigmentary usage.

3. The process of Claim 2 wherein the silica-containing material is an ammonium silicate.

4. The process of Claim 2 wherein the silica-containing material is a silicic acid.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,658,566 Dated April 25, 1972 Patent No.

SHEEHAN, GERARD MARTIN; ROBERTS, GEORGE LEATHWHITE, and

Inventor(s) DUPREE, PAUL MONTGOMERY It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

, under title Yellow Factor (2A) should read 5.65

Column Table II instead of "6.65"

Signed and sealed this 25th day of July 1972.

( EAL) Attest:

EDWARD M.F'LETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents USCOMM'DC 6037 6,-P69

i [1.5. GOVIIIIIIIIT IIIIITIIG OFFICE 1 ll! 0-JC-8S4 FORM PC4050 (10-69) 

2. A process for the preparation of the pigment of claim 1 which comprises treating a slurry of TiO2 with an aqueous solution of an aluminum salt to give an acidic slurry which is neutralized and admixed with a silica containing material in a proportion such that at least about 5 weight parts of silica is present for each part of alumina whereby a mixture of hydrous oxides of silicon and aluminum is precipitated; conditioning the coated TiO2 pigment by aging at a temperature ranging from 5* to 100* C. for a period up to about 24 hours; washing said conditioned pigment with water until it is substantially free of soluble salts; drying said pigment at an elevated temperature; and then milling said dried pigment until it has reached the desired degree of sub-division and is suitable for pigmentary usage.
 3. The process of Claim 2 wherein the silica-containing material is an ammonium silicate.
 4. The process of Claim 2 wherein the silica-containing material is a silicic acid. 